Double spiral antenna

Abstract

An antenna comprises a first antenna element, which has a first helix, and a second antenna element, which has a second helix. The first and the second antenna elements each have a feed point at an outer end of the corresponding helix and an open end at an inner end of the corresponding helix. A symmetrical helix antenna according to the invention can be integrated in a comparatively simple manner in an existing system, for example in a hearing aid. By integrating the antenna in a plastic housing, the antenna cannot be seen at all from the outside. The antenna is comparatively small in relation to conventional antennas.

1. An antenna for wireless data transmission, comprising:
 a first radiator that comprises a first spiral with a first feed point at an outer end of the first spiral and an open-circuit end at an inner end of the first spiral and functions as a first arm of a dipole antenna; and 
 a second radiator that comprises a second spiral with a second feed point at an outer end of the second spiral and an open-circuit end at an inner end of the second spiral and functions as a second arm of the dipole antenna, 
 wherein the first radiator and the second radiator are configured to:
 have a spatial gap between the first and the second radiators minimum in a range between 0.3 and 0.5 times a diameter of one of the first and the second spirals, 
 be coiled identically, 
 lie in a same plane or on a same material surface, 
 have a gap between the first feed point and the second feed point minimum of 5*10 −3  times a freespace wavelength at an operating frequency of the antenna. 
 
 
     
     
       2. The antenna as claimed in  claim 1 , wherein the gap between the first feed point and the second feed point is in a range between 0.4 and 0.6 times a diameter of one of the first spiral and the second spiral. 
     
     
       3. The antenna as claimed in  claim 1 , wherein a gap between a center of gravity of the first spiral and a center of gravity of the second spiral is greater than a hypotenuse of a right-angled triangle in which a first cathete has a length equal to half diameter of the first spiral and a second cathete has a length equal to half diameter of the second spiral. 
     
     
       4. The antenna as claimed in  claim 3 , wherein the center of gravity of the first spiral and the center of gravity of the second spiral are geometric centers of gravity of lines which follow a course of the first spiral and a course of the second spiral respectively. 
     
     
       5. The antenna as claimed in  claim 1 , wherein:
 the first spiral comprises a first spiral substrate area and a first spiral axis, 
 the second spiral has a second spiral substrate area and a second spiral axis, 
 a parallel projection of the first spiral substrate area in a direction of the first spiral axis does not intersect with the second spiral substrate area, and 
 a parallel projection of the second spiral substrate area in a direction of the second spiral axis does not intersect with the first spiral substrate area. 
 
     
     
       6. The antenna as claimed in  claim 1 , wherein the first radiator and the second radiator are electrically conductive. 
     
     
       7. The antenna as claimed in  claim 1 , wherein the first radiator and the second radiator are radiating slots. 
     
     
       8. The antenna as claimed in  claim 1 , wherein electrical characteristics at the first feed point and the second feed point are essentially symmetrical in relation to a reference potential. 
     
     
       9. The antenna as claimed in  claim 1 , wherein the first radiator and the second radiator are arranged on a surface of a dielectric material. 
     
     
       10. The antenna as claimed in  claim 9 , wherein the surface of the dielectric material is domed. 
     
     
       11. The antenna as claimed in  claim 1 , wherein the first radiator and the second radiator are integrated into a housing that comprises a dielectric material and houses an electronic circuit. 
     
     
       12. The antenna as claimed in  claim 11 , wherein the housing is a part of a behind-the-ear hearing aid. 
     
     
       13. The antenna as claimed in  claim 1 , wherein the operating frequency of the antenna is in a range between 500 MHz and 6 GHz. 
     
     
       14. The antenna as claimed in  claim 1 , wherein a maximum dimension of the antenna is 10 cm. 
     
     
       15. The antenna as claimed in  claim 1 , wherein a maximum dimension of the antenna is less than one fifth of the freespace wavelength at the operating frequency of the antenna. 
     
     
       16. The antenna as claimed in  claim 1 , wherein the antenna is used to wirelessly transmit data to a hearing aid.